Labour MP Jess Phillips said: “If he’s not sure then he should find out and rectify it as soon as possible. While tax affairs for ordinary people are a private matter, he is a Prime Minister who has committed to stamping out tax avoidance.”

And Labour leader Jeremy Corbyn will today tell supporters in Harlow, Essex: “The publication of the Panama Papers drives home what more and more people feel, that there is one rule for the rich and another for everyone else.

“It is time to get tough on tax havens. Britain has a huge responsibility, many of those tax havens are British overseas territories. As the leaked documents show, tax havens have become honey pots of international ­corruption, tax avoidance and evasion.

“The ­Government needs to stop pussyfooting around on tax dodging.”

Blairmore House, Cameron's ancestral home

HM Revenue and Customs is to probe claims of money laundering and tax avoidance following the leak of 11.5 million files outlining investments set up by ­Panama law firm Mossack Fonseca.

The papers were first handed to a German ­newspaper and then passed on to 107 global media outlets. Six peers, three former Tory MPs and ­political party donors were among 214,000 firms and individuals identified.

Blairmore, named after the Cameron family’s ancestral home in ­Aberdeenshire, was founded in the early 80s and still exists. It has managed tens of millions of pounds on behalf of wealthy clients.

They allegedly included Isidore Kerman – an adviser to disgraced media tycoon Robert Maxwell. The firm’s complex structure meant it kept up to 50 Caribbean officers each year who signed paperwork and filled roles such as treasurer and secretary. They are said to have included Solomon Humes, a Church of God of Prophecy bishop who was a vice-president. He has since died.

The Daily Mirror's front page on the Panama Papers

But files are said to show UK-based directors regularly held board meetings.

Former tax inspector and campaigner Richard Brooks said: “The clear intention for Blairmore was to avoid becoming UK tax resident and the test for this ... is the location of management and control.

“This means where the key ­business decisions are taken.

“The evidence here suggests in this period they weren’t taken outside the UK, in which case it is hard to see how the company was not managed and controlled, and therefore tax resident, in the UK.”

Blairmore were last night unavailable for comment. British companies feature as ­“intermediaries” more often than almost any other nation in the secret files. The British Virgin Islands was by far the most popular tax haven used.

He added: “The time has come to take away the keys, by requiring the publication of information on who owns the firms.”

Shadow Chancellor John McDonnell said: “Mr Cameron has promised to end tax secrecy and crack down on ‘morally wrong’ offshore schemes but has failed to do so.”

Money saving expert Martin Lewis said people should be paying tax “as part of the legitimate cost of living in a civil society”.

Lionel Messi insists the claims are "false" (Image: Getty)

Barcelona star Lionel Messi is mentioned in the papers but he insisted the claims are “false”. Tory donor Lord Bamford had a firm in the BVI which he closed before becoming a peer. No10 insisted Mr Cameron was “leading the pack internationally” on tackling tax-dodging.

Jennie Granger of HMRC said: “We have already received information on offshore ­companies, including in Panama, which is the subject of intensive investigation.”